I am sure that you already know this, but METAL BOXES - AT THE EDGE (book four) has been published on Kindle.
It is FREE on Kindle Unlimited
And
It’s only $2.99 to purchase in e-reader form.
It is available in print for $15.00 from CreateSpace and Amazon.
It should also be available on audiobook before the end of the year.
Metal Boxes - At the Edge
Alan Black